Line drivers are used to transmit data over a communication line to a receiver. The driver operates as a source that provides signals to the communication line, where the signals may be either differential or single-supply referenced. Either a current or voltage output signals may be provided, depending on the overall system requirements.
In one example system, the output signal from the line driver is provided as one or more single-supply referenced voltages. Data is transmitted over the communication line by pulling the voltage between one supply level (e.g., VCC) and another (e.g., ground). The receiver detects the voltage levels on the communication line to receive the data transmission.
In another example system, the output signal from the line driver is provided as a differential voltage that is provided to the communication line. Data is transmitted over the communication line by changing the polarity of the differential voltage from positive to negative. The receiver detects the polarity of the voltage on the communication line to receive the data transmission.
In still another example system, the output signal is a differential current that is driven into a terminating load at the opposite end of the communication line. Data is transmitted over the communication line by changing the polarity of the current from positive to negative. The current that is transmitted over the communication line is converted into a voltage by the terminating load. The receiver detects the changes in the polarity across the terminating load to receive the data transmission.
Many modern computing devices utilize transceiver interface circuitry. Two commonly used interfaces are the universal serial bus interface (USB) and the IEEE 1394 serial interface (also referred to as “Firewire”). Digital cameras, personal computers (PCs), personal data assistants (PDAs) are but a few example devices that often include a universal serial bus interface (USB). Digital video cameras, external hard disk drives, and PCs are but a few example devices that often include an IEEE 1394 interface.
Each transceiver circuit permits communication between two different devices over a serial communication link. The serial communication link is not a fixed bus, but instead is a configured by a user on demand. For example, a digital camera is a portable device that is not connected to a PC via a USB interface until data transfer is required. A USB cable serves as the communication bus that connects the digital camera to the PC such that the data can be transferred. Most LVDS devices can be “hot plugged”, meaning that the device need not be powered down before connecting the various devices together.